Ladders come in a variety of sizes. Short ladders, known as step ladders, have legs which make the ladder freestanding. Step ladders are generally not adjustable in height and come with a fixed number of steps. Longer ladders usually lean against a wall or outer building surface for support. Where a tall ladder is required, an extension type ladder is used that is made up of several segments, at least one of which is slidable relative to a base or lower ladder segment. By pulling on a cord or a cable, the extendable segment is moved relative to the lower segment, thereby extending the overall length of the ladder. A hooking arrangement is provided between the two segments to lock them together when a desired extension is achieved. This arrangement includes a hook like device on the moving portion, which engages the fixed base segment, for example, a rung or step to prevent the elevated segment from sliding back down. Thus, the extension ladder can be lengthened in incremental steps that correspond to the distance between adjacent ladder rungs.
Step ladders are easily operated and relatively safe for the average user, for example, the do-it-yourself person, working around the interior of the house. The major disadvantage of the step ladder is its fixed height and its major advantage is its small size, for use with low heights, and its supporting struts or legs which make the step ladder freestanding.
A disadvantage of the extension type ladder is the awkwardness in setting it up against a supporting wall, building side, tree limb, etc., and in operating the rope and latching devices for extending the ladder. Another disadvantage of the extension ladder is that it extends only in increments corresponding to the spacing between the ladder rungs. A further disadvantage is that the extension ladder is not freestanding. Therefore, when working at the center of a room, away from the walls, the extension ladder is not useful, and a worker must use scaffolding and the like when a step ladder is not of sufficient height.
What is needed is an all purpose ladder that can serve the functions of both a step ladder and also an extension ladder.